Investments (Tables)

9 Months Ended

Sep. 30, 2017

Investments [Abstract]

Marketable securities by security type

The following tables provide the Company’s marketable securities by security type as of September 30, 2017 and December 31, 2016 (in thousands):

	As of September 30, 2017
	Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Commercial paper and corporate bonds	$	388,062	$	14	$	(473	)	$	387,603
U.S. government agency debt securities	37,630		—		(56		)	37,574
Total	$	425,692	$	14	$	(529	)	$	425,177

	As of December 31, 2016
	Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Commercial paper and corporate bonds	$	389,459	$	4	$	(827	)	$	388,636
U.S. government agency debt securities	33,132		—		(65		)	33,067
Total	$	422,591	$	4	$	(892	)	$	421,703

Contractual maturities of marketable securities

Contractual maturities of the Company’s marketable securities as of September 30, 2017 and December 31, 2016 are summarized as follows (in thousands):

	As of September 30, 2017				As of December 31, 2016
	Cost		Estimated Fair Value		Cost		Estimated Fair Value
Due in one year or less	$	269,606	$	269,351	$	281,591	$	281,285
Due in one to five years	156,086		155,826		141,000		140,418
Total	$	425,692	$	425,177	$	422,591	$	421,703

Fair market value and gross unrealized losses of marketable securities

The following tables provide the fair market value and gross unrealized losses of the Company's marketable securities with unrealized losses, aggregated by security type, as of September 30, 2017 and December 31, 2016 (in thousands):

	In Loss Position for Less than 12 Months
	As of September 30, 2017					As of December 31, 2016
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Commercial paper and corporate bonds	$	261,519	$	(354	)	$	299,708	$	(771	)
U.S. government agency debt securities	16,302		(28		)	28,273		(59		)
Total	$	277,821	$	(382	)	$	327,981	$	(830	)

	In Loss Position for More than 12 Months
	As of September 30, 2017					As of December 31, 2016
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Commercial paper and corporate bonds	$	99,983	$	(119	)	$	68,158	$	(56	)
U.S. government agency debt securities	21,272		(28		)	4,794		(6		)
Total	$	121,255	$	(147	)	$	72,952	$	(62	)